1. Field of the Invention
The present general inventive concept relates to a flat panel display. More particularly, the present general inventive concept relates to a backlight unit having a point light source, and a flat panel display having the same.
2. Description of the Related Art
Generally, a flat panel display is classified into an emissive display and a non-emissive display. The emissive display, which actively emits light, includes a cathode-ray tube (CRT), a plasma display panel (PDP) and so on. The non-emissive display cannot actively emit light. A liquid crystal display (LCD) is a representative example of the non-emissive display.
The non-emissive flat panel display is able to show an image by receiving light from the outside. Thus, the non-emissive flat panel display needs a backlight unit, besides a display panel, to emit light to the display panel.
The backlight unit is divided into a direct light type and an edge light type according to a mounting position of a light source thereof. In the direct light type, the light source is disposed at a rear side of the display panel, thereby emitting light directly toward the display panel. The light source of the edge light type is disposed at lateral edges of a light guide plate to emit the light toward the display panel through the light guide plate. Since the edge light type is provided only at lateral edges of the display panel, brightness is deteriorated at the center in a wide display panel. For this reason, medium and large sized flat panel displays usually adopt the direct light type.
The light source used for the backlight unit includes a linear light source and a point light source. A cold cathode fluorescent lamp (CCFL) is a typical linear light source. A light emitting diode (LED) is a typical point light source. The CCFL has a large divergence angle and uniform optical patterns. However, the CCFL operated by AC signals requires an inverter and is subject to impact. Alternatively, although the LED does not require the inverter and is impact-resistant, a divergence angle of the LED is relatively smaller than that of the CCFL. With reinforced restrictions of the use of hazardous substances in producing goods, recently, the LED is drawing more attention than the CCFL because of the LCD containing harmful substances such as Hg, Ar and Ne.
FIG. 1 is a sectional view schematically illustrating a conventional non-emissive flat panel display with a backlight unit having a point light source.
As illustrated in FIG. 1, the conventional flat panel display 10 includes a display panel 11 displaying an image or picture therethrough, a backlight unit 12 mounted to a rear side of the display panel 11, and a base chassis 15 mounting various electronic parts and supporting the display panel 11 and the backlight unit 12. In addition, an optical sheet 16 is disposed between the display panel 11 and the backlight unit 12 to uniformly diffuse light emitted from the backlight unit 12 toward the display panel 11.
The backlight unit 12 includes a substrate 13 connected to the base chassis 15, and a plurality of light emitting diodes (LEDs) 14 mounted on the substrate 13. The substrate 13 is fixed to the base chassis 15, for example, by a screw S. The LEDs 14 has a relatively smaller divergence angle than the linear light source such as the CCFL. Therefore, the LEDs 14 are arranged at regular intervals so that the lights from each LED 14 are overlapped with one another.
FIG. 2 schematically shows divergence patterns of the lights generated from the LEDs 14.
Referring to FIGS. 1 and 2, the light of each LED 14 is diverged in a circular pattern and overlapped with the lights of adjacent LEDs 14. Accordingly, brightness decreases moving further away from the LED 14, and a dark spot D occurs at positions where the lights are less overlapping. Thus, when the light from the backlight unit 12 is emitted to the display panel 11 with partial brightness difference, bright lines may occur on a front side of the display panel 11. This problem can be solved, however, only partly by the optical sheet 16 disposed between the display panel 11 and the backlight unit 12.
As described above, in the conventional flat panel display which uses the point light source having a high light convergence and a small divergence angle, bright lines easily occur on the front of the display panel because of difficulty of emitting a uniform flat light to the display panel. Therefore, as well as the optical sheet, a predetermined space between the display panel and the backlight unit needs to be guaranteed in order to prevent occurrence of the bright lines. According to this, however, a thickness of the conventional LED flat panel display should increase compared to the CCFL flat panel display.
In addition, because the backlight unit of the conventional flat panel display is fixed on the base chassis using screws, such assembling is cumbersome. Furthermore, the screws penetrating the backlight unit and protruding backward on the base chasses further increase the thickness of the flat panel display.